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J.B. Dalton, T.L. Roush (NASA Ames Research Center), C.S. Jamieson (California Polytechnic, San Luis Obispo)
Current and planned spacecraft missions to Mars and the Outer Solar System rely on laboratory measurements to facilitate interpretation of remote-sensing data. Solar system objects typically occupy environments far from terrestrial ambient conditions. Compositional studies based on infrared spectroscopy are particularly dependent on laboratory work, as many planetary materials exhibit changes in spectral behavior due to extremes of temperature, pressure, and other influences. The conditions at the surfaces of icy satellites, for example, are difficult to reproduce except under tightly controlled specifications.
This is illustrated by comparing the visible and near-infrared reflectance of several materials measured at cryogenic temperatures. Water ice, which is of interest for most solid bodies of the outer solar system, exhibits strong temperature dependence, as does methane ice (Grundy and Schmitt, 1998; Grundy et al., 2002). Hydrated materials, such as salts anticipated to be abundant at Europa, and ammonia hydrates relevant to the Saturnian satellites, also display strong variations with temperature (Dalton and Clark, 1998; McCord et al., 1999; Dalton, 2001). Pyroxenes and olivines, found in rocky bodies including the moon, meteorites, and Mars, also change with temperature (Singer and Roush, 1985; Moroz et al., 2000; Hinrichs and Lucey, 2002).
We have initiated a program investigating temperature sensitivity of planetary materials in support of spacecraft missions. Measurements are performed in a cryogenic vacuum environment chamber with a compressed helium cryostat capable of maintaining temperatures as low as 10 Kelvin. We will report on materials such as sulfate hydrates, which display profound spectral changes at low temperatures, and other materials we have measured, such as calcium carbonate, iron sulfide, and tholins (Roush and Dalton, 2002). While many materials are expected to show only modest variations, careful measurement and analysis of planetary materials in the laboratory is necessary to confirm interpretations of remotely-sensed spectra of solar system objects.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.